Activating Both Basal Plane and Edge Sites of Layered Cobalt Oxides for Boosted Water Oxidation

Layered A_xCoO₂ materials built by stacking layers of CoO₂ slabs and inserting alkali ions in between them have shown a promising activity of oxygen evolution reaction (OER) due to their active edge sites. However, the large basal plane areas of the CoO₂ slabs show too strong adsorption energy to the reaction intermediates, which is unfavorable for the release of O₂. Here, a simple cation-exchange strategy based on Fe³⁺ and alkali ions is proposed to simultaneously activate both the basal plane and edge sites of A_xCoO₂ for the OER. X-ray absorption spectroscopy has revealed that the Fe³⁺ ions deposit both on the surface and edge sites of the CoO₂ slabs and enter the interlayer. The cation-exchanged A_xCoO₂ electrodes show a boosted activity compared to their pristine and conventional Fe-doped A_xCoO₂ counterparts. This phenomenon is mainly ascribed to the abundant edge-sharing Co–Fe motifs at the edge sites and the charge redistribution in the basal plane sites induced by the insertion of Fe³⁺ ions. This work provides a novel method to fully exploit layer-structured materials for efficient energy conversion.